1. Field of Invention
The invention relates to a wire-cut electric discharge machine, and in particular, to a wire-cut electric discharge machine capable of forming a workpiece with a taper including an extendable pipe which is provided between a frame and an upper wire guide to guide a wire electrode therein.
2. Description of Related Art
Conventionally, a wire-cut electric discharge machine is equipped with a wire electrode, a pair of an upper wire guide and a lower wire guide that supports the wire electrode across a workpiece, and a table moving mechanism that moves a table supporting a workpiece thereon in a horizontal direction at substantially a right angle relative to the length of the electrode. In electric discharge machining, the wire electrode is reeled out, guided near the surface of a workpiece by the upper and lower wire guides, and the table moving mechanism moves the table supporting the workpiece thereon in the horizontal direction. Arc electric discharging is repeatedly performed in between the wire electrode and the workpiece in insulated machining fluid, for example, resulting in electric discharge machining the workpiece.
Normally, the pair of wire guides is installed vertically, and the wire electrode guided by the wire guides, is also kept in tension vertically. When a workpiece is electrical discharge machined as above, a surface of the workpiece becomes vertical, however, when the pair of the wire guides is relatively moved in the horizontal direction, the wire electrode becomes slanted, and a processed surface of the workpiece can be electric discharge machined so that it can be tapered relative to a vertical direction.
The applicant of this application proposed a wire-cut electric discharge machine disclosed in Japanese Laid-Open Patent Publication No. 5-277836. In this wire-cut discharge machine, an automatic connection device that automatically connects a broken wire electrode is fixed to a frame at an upper part of the upper wire guide, and a vertically extendable pipe is provided in between the upper wire guide and the automatic connection device. Both ends of the pipe are respectively fixed to the automatic connection device and the upper wire guide. A wire electrode extending from the automatic connection device passes through the pipe and extends in the upper wire guide. The upper wire guide can be moved upward and downward by the wire guide lifting mechanism.
Since the wire-cut discharge machine provides the pipe, the machine gains a function of enabling the wire electrode to be guided to the upper wire guide on the occasion when a broken wire electrode is automatically connected. Therefore, the automatic connection device is mounted to the frame fixedly above the upper wire guide. Compared with the original conventional machine where the automatic connection device is raised and lowered along with the upper wire guide, a wire guide lifting mechanism is smaller, and deterioration of the automatic connection device due to stains of machining fluid can be prevented.
When workpieces are electrical discharge machined so that their processed surfaces can be tapered relative to the vertical direction, the wire electrode between the pair of wire guides needs to be inclined from the vertical direction. For this purpose, the upper wire guide needs to be moved horizontally because it is difficult to move the lower wire guide only in the horizontal direction.
In the wire-cut electric discharge machine described in Japanese Laid-Open Patent Publication No. 5-277836, however, both ends of pipe are fixedly linked to the automatic connection device and the upper wire guide respectively, and the upper wire guide is not allowed to move horizontally. Therefore, electrical discharge machining cannot be applied to workpieces, so that their processed surfaces become tapered inclined from the vertical direction.
To allow the upper wire guide to move horizontally, it is possible to omit the pipe in the machine. However, this is not desirable from a safety standpoint because the wire electrode therebetween is exposed to the outside, and the automatic connection device may not able to operate correctly because the wire electrode is not guided to the upper wire guide.
On the other hand, it is possible to make the automatic connection device rise and lower along with the upper wire guide by installing the automatic connection device to the upper wire guide. However, it becomes difficult to shrink the size of the wire guide lifting mechanism and prevent the automatic connection device from deteriorating due to stains of machining fluid.